1. Field of the Invention
The present invention relates to a flat type color cathode ray tube, and more particularly, the present invention relates to a flat type color cathode ray tube of high quality, which is capable of guaranteeing brightness uniformity while improving contrast, thereby ensuring flatness and visual distinction of an image.
2. Description of the Related Art
Referring to FIG. 1, there is shown a partially sectioned side view schematically illustrating a construction of a color cathode ray tube. The color cathode ray tube includes a panel 1 defining a front surface of the cathode ray tube, a shadow mask 3 performing a function of selecting colors of emitted electron beams 11 in the panel 1, a frame 4 for fastening and supporting the shadow mask 3, a stud pin 6 for securing the frame 4 to the panel 1, a spring 5 for connecting the stud pin 6 and the frame 4 with each other, a funnel 2 coupled to a rear end of the panel 1 to maintain the inside of the panel 1 under a vacuum pressure, a tubular neck section 10 extending rearward from a rear end of the funnel 2, an electron gun 8 mounted in the neck section 10 to emit electron beams 11, an inner shield 17 assembled to the frame 4 to protect the emitted electron beams 11 from an external magnetic field, a deflection yoke 9 surrounding a circumferential outer surface of the funnel 2 to deflect the electron beams 11, a reinforcing band 12 for preventing implosion of the cathode ray tube maintained under a high vacuum pressure, and a lug 13 for fastening the reinforcing band 12 to the cathode ray tube.
Curvatures of inner and outer surfaces of the panel 1 influence an implosion-resistant characteristic and visual distinction of an image displayed on the panel 1.
In particular, a curvature of the inner surface of the panel 1 significantly affects flatness and distortion of an image, to thereby influence the visual distinction. Also, the curvature of the inner surface of the panel 1 affects a transmittance of the panel 1 and transmittance formation, so as to ensure brightness uniformity and allow light and dark regions on a picture image to be easily distinguished. That is to say, a precise inner surface curvature of the panel 1 plays an important role in realizing a cathode ray tube of high quality.
In the cathode ray tube constructed as mentioned above, the electron beams 11 emitted from the electron gun 8 are deflected by the deflection yoke 9 and then pass through apertures defined in the shadow mask 3, in a manner such that they are impinged onto fluorescent materials applied on the inner surface of the panel 1 and respectively aligned with the apertures of the shadow mask 3, to display a picture image.
At this time, a contour of the picture image is determined by the inner and outer surfaces of the panel 1. In other words, depending upon curvatures of the inner and outer surfaces of the panel 1, when a picture image initially created by emitting electron beams onto the fluorescent materials applied to the inner surface of the panel 1 passes through the panel 1, a contour of the picture image is changed by refraction of light, and the resultantly displayed picture image has a curved contour depending on the curvatures of the inner and outer surfaces.
It is to be noted that excellent clarity of a picture image displayed on the cathode ray tube can be accomplished by ensuring brightness uniformity and allowing light and dark regions to be easily distinguished on the picture image, depending upon a transmittance as well as a curvature of the panel 1.
Recently, the ever increasing demand for a large-sized flat cathode ray tube has led to enlargement and flattening of the panel 1. FIG. 2a is a side cross-sectional view independently illustrating a contour of a curved panel which has curvatures on both inner and outer surfaces thereof; and FIG. 2b is a side cross-sectional view independently illustrating a contour of a flat panel which has a curvature only on an inner surface thereof.
An inner surface curvature of a panel can be expressed by a xe2x80x9cwedge ratexe2x80x9d which is a thickness ratio between a center part and a diagonal end part of the panel. As can be readily understood from FIG. 2b, the conventional flat panel having a curvature only on an inner surface thereof possesses a wedge rate of no less than 200%. When considering the fact that the conventional curved panel having curvatures on both inner and outer surfaces thereof possesses a wedge rate of about 130%, the conventional flat panel tends to be overly increased in its thickness at a peripheral part thereof, especially at the diagonal end part. Consequently, as a difference between transmittances of the center part and the peripheral part is increased, when a picture image is created on the panel, a remarkable difference exists between brightnesses of the center and peripheral parts, so that eye strain is caused.
To cope with this problem, a method has been disclosed in the art, in which a panel is formed to have at a center part thereof a high transmittance of no less than 85%. By this method, even though a thickness is increased at the peripheral part of the panel, since a transmittance is not decreased at the peripheral part, it is possible to maintain brightness uniformity.
While capable of maintaining brightness uniformity of a picture image, this method has disadvantages in that, since an excessively high luminance is produced over an entire surface of the picture image, strain of the eye is increased. Also, because an unfavorable phenomenon which deteriorates contrast as a distinguishability between lightness and darkness results in, when a cathode ray tube is turned on under a bright surrounding condition, eye strain occurs. Further, in this bright surrounding condition, even when the cathode ray tube is turned off, a favorable viewing condition cannot be rendered.
In order to overcome these disadvantages, a brightness of the picture image as a whole should be decreased. To this end, there have been disclosed in the art techniques of applying a coating on the panel for the purpose of adjusting a transmittance and attaching a film having a low transmittance to the panel. Nevertheless, these techniques still encounter problems in that additional processes and manufacturing costs are incurred to form the panel.
Further, in the case of decreasing a transmittance only at the center part of the panel with an aim of enhancing a contrast between light and dark regions, because the conventional cathode ray tube has a wedge rate of 200%, which is calculated as a thickness ratio between the center part and the diagonal end part of the panel, a transmittance is decreased at the peripheral part, and thereby, brightness uniformity of the picture image cannot be guaranteed.
Accordingly, the present invention has been made in an effort to solve the problems occurring in the related art, and an object of the present invention is to provide a flat type color cathode ray tube of high quality, which is capable of maintaining a brightness and brightness uniformity of an image while improving contrast as a distinguishability between lightness and darkness, thereby ensuring flatness and visual distinction of the image.
In order to achieve the above object, according to one aspect of the present invention, there is provided a flat type color cathode ray tube comprising: a rectangular panel having an outer surface which is substantially flat and an inner surface which takes a predetermined curvature, the rectangular panel being formed with a skirt part which extends substantially perpendicularly to the inner and outer surfaces; a shadow mask for performing a function of selecting colors of emitted electron beams in the panel; a frame for applying tensioning force to the shadow mask and supporting the shadow mask; a funnel coupled to a rear end of the panel to maintain the inside of the panel under a vacuum pressure; a tubular neck section extending rearward from a rear end of the funnel; an electron gun mounted in the neck section to emit electron beams; and a deflection yoke surrounding a circumferential outer surface of the funnel to deflect electron beams; wherein the panel possesses at a center part thereof a transmittance of 45%xcx9c75%, and the inner surface of the panel possesses an on-diagonal-axis curvature RD which satisfies the following inequality (1):
3.5Rxe2x89xa6RDxe2x89xa68.0Rxe2x80x83xe2x80x83(1).
According to another aspect of the present invention, there is provided a flat type color cathode ray tube comprising: a panel having an outer surface which is substantially flat and an inner surface which takes a predetermined curvature, the inner surface of the panel possessing an on-major-axis curvature RX, an on-minor-axis curvature RY and an on-diagonal-axis curvature RD which respectively satisfy correlations, 4.5RXOxe2x89xa6RXxe2x89xa68.0RXO, 2.5RYOxe2x89xa6RYxe2x89xa68.0RYO and 3.5RDOxe2x89xa6RDxe2x89xa68.0RDO.
According to still another aspect of the present invention, there is provided a flat type color cathode ray tube comprising: a panel having an outer surface which is substantially flat and an inner surface which takes a predetermined curvature, the panel possessing at a center part thereof a transmittance of 45%xcx9c75%, the panel further possessing a wedge rate as a thickness ratio between the center part and a diagonal end part of the panel, which satisfies a correlation, 1.4xe2x89xa6wedge ratexe2x89xa62.0.